This application is based upon Japanese Patent Application No. Hei. 11-74024 filed on Mar. 18, 1999, the contents of which are incorporated herein by reference.
1. Field of the Invention
This invention relates to navigation systems, and particularly to a vehicular navigation system which performs travel guidance regarding an intersection existing on a recommended guidance route when a vehicle approaches the intersection.
2. Related Art
Various navigation apparatuses for adequately guiding a vehicle to a destination, by detecting a present position of the vehicle by using a GPS or the like and by displaying the present position on a display with a road map,have been proposed. Furthermore, the other navigation apparatuses for setting an adequately route (a recommended guidance route) from the present portion to the destination and for performing route guidance have been proposed.
In this kind of navigation apparatus, some apparatuses perform travel guidance with voice sound regarding an intersection existing on a recommended guidance route when a vehicle approaches the intersection. For example, some apparatuses guide using both a distance to the intersection and a direction to be turned, with verbal instructions such as xe2x80x9cAfter ◯◯ meters, please turn rightxe2x80x9d. Furthermore, some apparatuses further guide with respect to a name of the intersection, with verbal instructions such as xe2x80x9cAfter ◯◯ meters, please turn left at intersection of xe2x96xa1xe2x96xa1.xe2x80x9d It is convenient for the user when the navigation apparatus timely notifies with verbal instructions, because the user does not need to pay attention to the relationship between the present position and the intersection.
In this case, the intersection to be guided means not all the intersections existing on the recommended guidance route, but only particular intersections at which the user may deviate from the recommended guidance route if there is no guidance regarding the direction to be turned. Therefore, this kind of apparatus basically performs xe2x80x9cFollowing-the-road judgmentxe2x80x9d, which judges whether the vehicle turns at the particular intersection or not, with respect to each of the particular intersection.
However, it cannot always say that it is not xe2x80x9cFollowing-the-roadxe2x80x9d when a road shape is merely curved. For example, when a narrow side road is connected to a wide main road at a point of the main road where the main road is about to curve, a route along the main road can be called xe2x80x9cFollowing-the-road.xe2x80x9d From a standpoint of the user, he/she merely continues to travel a road on which he/she has been traveled. Therefore, the apparatus performs the xe2x80x9cFollowing-the-road judgmentxe2x80x9d by largely considering a fact whether a continuity of the road is secured between before and after the intersection. When the continuity is not secured, the apparatus regards this situation as not xe2x80x9cFollowing-the-roadxe2x80x9d, and decides the intersection as the intersection to be guided.
For example, as shown in FIG. 6, it is assumed that a vehicle travels a main lane of a highway or an automobile specialized road, and that there is an on-ramp or an off-ramp connected to an interchange (IC), a service area (SA) or a parking area (PA). In this case, according to a conventional navigation apparatus, a branch point at which the off-ramp is connected to the main lane and a merge point at which the on-ramp is connected to the main lane are not regarded as the intersection to be guided. In other words,when there recommended guidance route is determined so that the vehicle travels along the main lane, but does not travel to the off-ramp, the conventional navigation apparatus does not perform the travel guidance, because this condition is actually the, xe2x80x9cFollowing-the-road.xe2x80x9d This is because it is confusing for the user when the travel guidance is performed at every time he/she approaches the IC, the SA or the PA, although he/she does not intend to deviate from the main lane. Here, some conventional navigation apparatus performs the guidance with voice sound such as xe2x80x9cAbout 5 kilometers ahead, you will find a SA (or a PA) xe2x80x9d to inform the user of an existence of the SA or PA, however, this type of navigation apparatus simply informs the existence thereof. Therefore, such guidance is performed ahead of some kilometers (e.g., 5 kilometers). Further explanation regarding this type of navigation apparatus is omitted, because this is another technical field from the travel guidance to be pointed out as a problem.
However, when the travel guidance is not performed as a result of a decision that it is the xe2x80x9cFollowing-the-roadxe2x80x9d in the conventional Following-the-road judgment, the user may become confused because the road has a unique shape. An example of such a unique-shaped road will be explained with reference to FIGS. 2A and 2B.
As shown in FIG. 2A, when a merge point, at which an on-ramp from the SA or the PA is merged (connected) with a main lane, is provided close to a branch point, at which an off-ramp to the IC or the SA is branched from the main lane, it can be thought that the number of lanes is increased only between the merge point and the branch point. Here, as shown in FIG. 2B, in general, the number of lanes is increased only for a predetermined distance from the merge point to smoothly merge traffic; and the number of lanes is also increased only for a predetermined distance before the branch point to smoothly branch the traffic. As a result, when the merge point is provided close to the branch point, the increased lane is continuously provided. Actually, this type of road is seen in Europe.
Normally, the road has a shape so that traffic on the increased lane is automatically merged to the main lane (the temporarily increased lane is decreased again). However, according to the above-described example, since the number of lanes is not decreased, the vehicle may keep on traveling on the increased lane. Of course there is no problem if the user is well acquainted that he/she travels on such a unique road. Therefore, it is preferable for a vehicular navigation system to perform the travel guidance even if the road on which the user travels has such a unique shape.
Although FIG. 2A is a typical example of the unique shaped-road, it can be though that it needs to perform some travel guidance even if the user travels the unique shaped-road, which is not regarded as the intersection to be guided in the regular Following-the-road judgment due to its unique shape.
This invention has been conceived in view of the background thus far described and its first object is to improve usefulness of route guidance.
Its second object is to improve usefulness of route guidance, so that among intersections, which are not regarded as the intersections to be guided in the Following-the-road judgment, a particular intersection to which travel guidance is to be performed can be adequately judged as the intersection to be guided.
According to the present invention, following-the-road judgment means judges whether a continuity of a travel road is secured before and after the intersection when a vehicle passes through a particular intersection existing on a recommended guidance route, and determines the particular intersection as an intersection to be guided when the continuity of the travel road is not secured. Even when the particular intersection is not determined as the intersection to be guided by the following-the-road judgment means, ramp judgment means determines the particular intersection as the intersection to be guided, when the particular intersection is a branch point at which an off-ramp is connected to a main lane to divide traffic on the main lane to the off-ramp, and when there is a merge point at which traffic is merged to the main lane within a predetermined distance ahead from the branch point, and further when the recommended guidance route is set so that the vehicle keeps on traveling on the main lane. Travel guidance performing means performs travel guidance regarding the intersection to be guided, which is determined by one of the following-the-road judgment means and the ramp judgment means, when the vehicle approaches the intersection to be guided.
According to the above-described structure, since the ramp judgment means judges as the above ways, the travel guidance is adequately performed to the branch point, which is not judged as the intersection to be guided only by the xe2x80x9cFollowing-the-road judgmentxe2x80x9d.
According to another aspect of the present invention, even when the particular intersection is not determined as the intersection to be guided by the following-the-road judgment means, the ramp judgment means determines the particular intersection as the intersection to be guided, when the particular intersection is a branch point at which an off-ramp is connected to a main lane to divide traffic on the main lane to the off-ramp, and when the number of lanes including the main lane is decreased after the particular intersection.
According to the above-described structure, since the ramp judgment means judges as the above ways, the travel guidance is adequately performed to the branch point, which is not judged as the intersection to be guided only by the xe2x80x9cFollowing-the-road judgmentxe2x80x9d.